The present invention relates generally to electronic device packaging assemblies and, more particularly, to an electronic device packaging assembly having spacers for maintaining base and cover substrate portions of the package assembly in parallel relationship with a lead frame portion of the assembly.
In many electronics applications, it is necessary to house an electronic device such as an integrated circuit chip within a protective casing in order to protect the electronic device from the environment. Electronic device packages are disclosed in U.S. Pat. 4,897,508 of Mahulikar et al. which is hereby specifically incorporated by reference for all that it discloses.
A typical electronic device package assembly comprises a relatively flat lead frame having a plurality of leads terminating at an interior opening. The electronic device to be housed is positioned in alignment with the interior opening of the lead frame and is electrically attached to the interior terminal ends of the leads by connecting wires. The bottom portion of the lead frame is bonded by a ring of matrix material to a base substrate member and the top of the lead frame is bonded by a ring of matrix material to a cover substrate member. The electronic device is thus maintained within an enclosure defined by the base substrate member, the cover substrate member, and the two rings of matrix material. The base substrate and cover substrate are generally of the same size and shape and are aligned with one another. The leads of the lead frame extend radially outwardly between the two rings of bonding material, typically to a position beyond the outer periphery of the base and cover substrate members. The exposed outer ends of the leads enable the electronic device to be electrically connected to other components.
During the formation of such an integrated circuit package, the bonding material is typically applied in a viscous liquid form, one ring at a time, with heat curing steps following each application of bonding material. In many applications, the electronic device package assembly must be constructed within precise tolerances. One problem experienced in the construction of such electronic package assemblies is that due to the lack of rigidity in the bonding rings during assembly, it is difficult to maintain the base and cover components in exact parallel alignment.
As a result of this problem, holding fixtures have been developed which employ a machine spacer to hold the base and cover substrates in parallel alignment during fabrication. However, a problem with this solution is that the holding fixtures are relatively expensive to produce and are cumbersome in operation. A further problem is that the holding fixtures does not hold the central plane of the lead frame in parallel alignment with the base and cover plates. As a result of this non-parallelism of the lead frame, some of the outer lead terminals are positioned nearer to the base member and others of the outer lead terminals are positioned closer to the cover member. A package assembly thus constructed is often rejected during an initial testing for accuracy of dimensional parameters due to the misalignment of the lead frame with the base and cover members. Even if the package assembly passes the initial dimension testing, it is likely to fail subsequent electrical testing because of uneven contact with electrical test sockets. Furthermore, misalignment of the lead frame with the base and cover member may cause some of the leads to be bumped during handling causing the leads to be further misaligned or damaged. As a result, the assembly may fail further electrical testing or may cause a failure of an associated circuit board, etc., when the device is mounted for use in its intended application.
Thus, a need exists for an electronic device package assembly which may be constructed with the base plate, the cover plate, and the central plane of the lead frame located in parallel alignment. The method by which such an assembly is constructed should preferably be cost efficient and relatively easy to implement.